JPH0568978B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] The present invention relates to computed axial tomography (CAT) scanners, and more particularly to the type using a continuously rotating gantry.
It concerns CAT scanners.

[Conventional technology]

CAT scanners utilize a rotating gantry to obtain multiple x-ray images, or "views," at progressively different rotation angles. Each set of images is called a "slice" in this technology.
The patient lies on an axially movable table within the central opening of the gantry, allowing slices to be obtained at multiple axial positions.

All obtained slices are processed in a computer according to known algorithms to produce an enhanced image for diagnosis.

The rotating gantry contains the x-ray equipment and the necessary electronics to generate the video data for each view. There is therefore a need to power the rotating gantry in order to power the electronic equipment, and in particular to provide a high voltage source for the operation of the x-ray tube. It is also necessary to communicate video data and other control information between the electronics on the rotating gantry and a set of stationary electronics. A stationary electronic device processes the raw video data into an enhanced aspect. Data speed for communication between stationary and rotating electronic devices is an important factor. This is because it is desirable to obtain the desired view as quickly as possible to reduce patient discomfort and maximize device utilization. Since a view typically has 730 channels and each individual channel output is a 16-bit representation (i.e., 11.68K bits per view) and is typically repeated 1000 times per second, the video This results in a net data rate requirement of approximately 12 megabits/second (Mbit/second) for data alone.

To provide a communications link at the required data rates, traditional CAT scanners employ an umbilical cable connected to a rotating gantry. The cables used one or more shielded flexible coaxial cables for high speed communications and other conductors to carry power supply and other discrete control signals. Since the umbilical cord cable can rotate plus or minus 360 degrees, the entire gantry is limited to 360 degrees of rotation. During operation, the gantry is accelerated to the desired rotational speed and obtains the desired view by the time the 720 degree limit is reached. Near the limit of 720 degrees,
The gantry is slowed to a stop and then accelerated in the opposite direction to get more views. Therefore, the gantry cycles back and forth within the 720 degree limit.

Such "repetitive" type CAT scanners have 2
There are two major drawbacks. One drawback is that deceleration and reacceleration of the gantry takes considerable time. A gantry with all equipment installed in a predetermined location is large and heavy, so even with a large motor it takes a long time to accelerate the gantry. Second
The drawback is somewhat a corollary of the first drawback that the need to repeatedly accelerate such large masses results in high mechanical strain and wear.

Other types of gantries are also known that use brushes and slip rings for power supply and communication. In that case, the gantry rotates freely and continuously, eliminating the need for the above-mentioned back and forth rotation of the gantry,
This allows most of the time to be used to acquire desired views. However, conventional CAT scanners that use brush slipping for communication suffer from severe limitations in the data rates that can be achieved. The gantry and its attached slip springs are necessarily large and unshielded. Therefore, the slip ring is subject to significant external electrical noise. However, the bigger problem is providing high data rate communications. In that case, a very high edge rate is required for the signal applied to the slip ring, but the round trip time interconnecting around the slip ring is much longer than the edge rate; This results in an unstable vibration response. Also, because the electrical path length around the ring is a significant fraction of the bit period, the energy traveling back through the ring can arrive at the receiving point at widely different times during the bit period, resulting in This will result in incorrect reception.

[Problem to be solved by the invention]

Therefore, there is a need for a high speed communication device for a CAT scanner that provides continuous rotation and reliable high speed communication.

The purpose of the invention is to suppress extraneous noise in slip rings for reliable communication at high data rates.

Another object of the invention is to substantially eliminate common mode noise by utilizing a third slip ring in conjunction with the second slip ring to supply the operating voltage to the receiving means. .

[Means to solve the problem]

The communication device of the present invention includes a stationary electronic device installed on a stationary stand, and a movable electronic device installed on a rotating stand that can perform rotational movement about a rotating axis with respect to the stationary stand. High-speed communication is performed with the device. A slip ring for signal voltage transmission is arranged coaxially with the rotating shaft on the rotating table. An electrical signal voltage is transmitted from a drive circuit connected to a stationary electronic device (or a mobile electronic device) to a signal voltage transmission slip ring at its drive point via a brushed sliding contact (or a physical normal electrical connection). ). The electrical signal voltage is referenced to a signal ground reference potential and is encoded by data transmitted from the stationary (or mobile) electronic device.

In order to passively terminate the electrical signal voltage in the slip ring for transmitting the signal voltage, a termination circuit is provided on the base on which the stationary electronic device (or the mobile electronic device) is located. The electrical signal voltage applied at the driving point is transferred by the resistive termination of the termination circuit to the terminal point of the signal voltage transmission slip-ring via a brushed sliding contact (or via a physical normal electrical connection). ) Terminate. The termination point faces the driving point approximately on the diameter of the signal voltage transmission slip ring.

A receiver circuit is provided connected thereto for receiving and transmitting the electrical signal voltage on the signal voltage transmission slip ring to the mobile electronic device (or stationary electronic device). The electrical signal voltage on the signal voltage transmission slip ring is conveyed to the receiving circuit via a physical conventional electrical connection (or via a brushed sliding contact).

An advantage of the present invention is that very high data rate communications can be achieved through large diameter slip rings. A resistive termination at a termination point approximately diametrically opposite the drive point electrically separates the slip ring into two paths around its circumference. Those paths can be thought of as two separate transmission lines,
Each transmission line can be properly terminated. Energy traveling in opposite directions through the slip ring meets at the termination point and cancels each other out, so there is virtually no reflected energy or energy traveling to the opposite path.

For effective cancellation, the impedance of the resistive termination can be approximately equal to the impedance of the slip ring as seen from the termination point. Furthermore, the source impedance of the drive circuit can be made approximately equal to the impedance of the slip ring viewed from the drive point, thereby increasing the effect of suppressing reflected energy.

A second slip ring can be provided to better approximate the characteristics of the transmission line for the signal voltage transmission slip ring. The second slip ring is called a ground reference slip ring, and is provided on the turntable coaxially with and close to the signal voltage transmission slip ring. A signal ground reference potential from a drive circuit connected to a stationary electronic device (or a mobile electronic device) is applied to the ground reference slip ring at a point approximately co-linear with the drive point (this is the drive point of the ground reference slip ring). ), through a brushed sliding contact (or through a physical conventional electrical connection). The signal earth reference potential used for the resistive termination of the termination circuit is a point approximately collinear with the termination point to the earth reference slip ring (this is the termination point of the earth reference slip ring).
(or through a physical normal electrical connection). Here, the driving point and the terminal point of the ground reference slip ring face each other approximately on the diameter of the ground reference slip ring.

〔Example〕

First, referring to FIG. 1, the computerized axial tomography (CAT) scanner includes a stationary table that includes a stationary electronic device 30, etc., and a rotating gantry 11 that is a rotary table that can rotate with respect to the stationary table. include.

The rotating gantry is provided with a central hole 12 large enough to receive a patient 13. The patient 13 is supported on a platform 14 that can slide axially, ie, move in and out of the central hole 12. Gantry 11 also includes an x-ray tube 15. The x-ray tube includes a thin sector X, generally indicated by dashed line 16.
A beam forming device for generating a line beam is combined. The beam 16 traverses the central hole 12 and
It penetrates the patient 13 contained therein and enters the detector array 20 . The detector array is curved and has a resolution of 730 channels along its length. The individual outputs of each channel of detector array 20 are connected in parallel to data acquisition device DAS 21. Each sampled channel output is converted by the DAS into a 16-bit digital value representing the intensity of the x-rays.

Gantry 11 also includes electronic equipment 25 . This electronic device 25 is a movable electronic device that rotates together with the gantry 11, and controls the operation of the X-ray tube 15,
It includes circuits necessary for collecting video data obtained by the DAS 21. In particular, the electronic device includes a high voltage section 26 and a control section 27. Control unit 27
includes a computer (not shown). The control is subordinate to the stationary electronics 30. This electronic device 30 is of course provided apart from the gantry 11.
The stationary electronics 30 is a computer-based device for issuing commands to the control 27 on the gantry 11 and for receiving and processing the resulting video data.

The present invention provides a communication system for coupling stationary electronics 30 to rotational control 27 by using large diameter slip rings and brushes that allow continuous rotation of gantry 11. As mentioned above, the minimum required data rate for video data only is on the order of 12 megabits (MB)/second. In this example,
A total datalet of 55 MB/sec is preferred in order to handle other communication data in addition to video data in a time-sharing manner and to take communication overhead into account. In the future, higher data rates, e.g.
On the order of 125MB/s is desired as detection and processing performance increases. Such high data rates have not heretofore been possible with large diameter slip rings. The present invention overcomes that limitation by allowing very high speed communications even with the large diameter slip rings of CAT scanners.

In the following description, all communications between the stationary electronics 30 and the control unit 27 are serialized using conventional multiplexing techniques, e.g. converted from parallel data to serial data for transmission, and that serial data is being converted to parallel data for reception. It is done so that only one bit stream needs to be sent. However, it will be clear to those skilled in the art that a large number of parallel paths of the invention can be used, for example, to further increase the maximum achievable data rate.

Several sets of slip rings and brushes are actually used in this embodiment, as will be explained in more detail below. However, for simplicity, the slip ring is generally represented by a circle 31 in FIG. This circle defines the outer boundary of the gantry 11. A conventional brush (not explicitly shown in FIG. 1) is used to apply modulated power to slip ring 31 to represent the serial data to be communicated.

The diameter of the slip ring 31 is approximately 1.21m.
(4 feet), with a circumferential length on the order of approximately 3.83 m (12.56 feet). Furthermore,
The bandwidth required to reliably transmit at the preferred data rate of 55MB/s, including modulation sidebands, is
It is on the order of 400Mhz. Because the dimensions of the slip ring are very large and the data rates involved are very high and the rise times or required edge rates are correspondingly very short, the slip ring 31 is treated as a high frequency transmission line.
This transmission line can be modeled as shown in Figure 1a.

Next, referring to FIG. 1a, slip ring 31
is modeled by two transmission lines 31a and 31b of equal length. The characteristic impedance of each transmission line is Z ₀ and constitutes half of the slip ring 31. In the actual embodiment described below, the actual slip ring 31 is a parallel curved conductor, more similar to a two-wire or multi-wire transmission line. However, the coaxial line shown in FIG. 1a can still be used for the intended purpose.

When high frequency energy is applied to a single drive point 40 on slip ring 31, the energy is split and directed simultaneously around transmission lines 31a and 31b in both directions, e.g., clockwise orientation 41a and counterclockwise orientation 41b. Conveyed. In theory, the signal picked up by slip ring 31 would be highly position dependent and distorted, since the effect of high frequency energy traveling in opposite directions around a large diameter slip ring would be such that it would create an interference pattern. It will be done. This effect is the main reason why conventional large diameter slip rings are unsuitable for high speed communications.

In the present invention, terminator 43 connects to termination point 44 via another set of brushes. This termination point 44 is 180 degrees opposite the drive point 40. Terminator 4
3 at the 180 degree termination point 44, the split energies traveling in opposite directions along the ring 31 meet at the terminator 43 almost simultaneously.
Terminator 43 has a resistance approximately equal to Z ₀ /2 so that the parallel combination of transmission lines 31a and 31b is impedance matched to terminator 43 without reflected energy. Two transmission lines 31a and 3
Since the path lengths of the lines 1b are approximately equal, the energy generated at the driving point 40 reaches the terminator 43 in unison, so that the energy does not continue to be transmitted through the opposing transmission lines 31a and 31b, respectively.

Considering the brush contact points utilized in this embodiment, it should be noted that a conventional brush is utilized which typically employs multiple spring-loaded contact leaves that contact the slip ring at many points of approach. It is. Although multiple leaf brush assemblies actually touch multiple points, many of the points are close enough to each other compared to the circumference of a large slip ring that they are functionally considered one point. be able to. Of course, one leaf brush can be used with the present invention. In this case there is only one actual contact point per bush. In the following description, the term "point" will therefore be understood to mean one or more closely spaced contact points by the brush assembly.

Referring again to FIG. 1, the split transmission line model described above is applied in two ways in the following embodiments. The first embodiment concerns the incoming channel. In this case, the input drive circuit 45 is slidably connected to the slip ring 31 via a brush (not shown in FIG. 1). What is the connection point between the input and termination circuit 46 and the input drive circuit 45 via the brush?
It is connected to the slip ring 31 at 180 degrees different points. Input drive circuit 45 receives a serial input signal from stationary electronics 30 via input cable 47 . This input signal is amplified and then sent to slip ring 31. As in the transmission line model, the transmitted energy is split and transmitted around the slip ring 31 in two directions, 180
terminated at different points. Therefore, this signal is sent to the slip ring 31 for reception.
Available anywhere in .

An input/receive circuit 48 is provided on the rotating gantry 11 and physically connected to a fixed point on the slip ring 31. The input/reception circuit picks up the signal sent by the input drive circuit 45, buffers it, and couples it to the control section 27 via a cable 49. The entire gantry 11 is connected to the input drive circuit 4
5 and the input/termination circuit 46, the static circuit 45
The actual position of the incoming/receiving circuit 48 relative to and 46 can be any position on the slip ring 31.

Still referring to FIG. 1, the second embodiment relates to an outgoing communication path from the control unit 27 in the gantry 11 to the stationary electronic device 30. In this embodiment, the drive connection and the termination connection are physically provided on the slip ring 31, and the reception connection is made via a brush. In particular, for outgoing communication, a serial signal is coupled from control 27 via cable 56 to drive circuit 55 . Output drive circuit 55
Since it is provided in the gantry 11, a physical connection is made from the output drive circuit 55 to the slip ring 31. In order to terminate the drive signal generated by the output drive circuit 55 as described above, an output termination circuit 57 is similarly connected to a point of the slip ring 31 that is 180 degrees different from the connection point to the output drive circuit 55. . A stationary output/reception circuit 58 is then connected to the slip ring 31 via brushes and coupled to the stationary electronics 30 via a receive signal cable 59.

Referring again to FIG. 1, another aspect of the invention includes controlling noise in the slip ring and maintaining electrical isolation between the stationary electronics 30 and the controller 27. For those reasons, separate and separate DC power supplies 65 are provided to power the incoming and outgoing communication circuits. As will be explained in detail later, separate slip rings are provided for communication signals, called signal slip rings, and for DC power supply voltages, called power slip rings (see FIG. 1). although not shown separately). Power supply slip rings provide dc power supply voltage to various drive circuits, receiver circuits, and termination circuits. In particular, the power supply voltage is
(a) from power supply 65 via cable 66 to input drive circuit 45; (b) from input drive circuit 45 via first power supply slip ring set (not shown separately in Figure 1); To circuit 48, (c) input/reception circuit 4
8 to the output drive circuit 55 via the cable 67,
and (d) is sequentially supplied from the output drive circuit 55 to the output/reception circuit 58 via a second power supply spring set (also not separately shown in the figure). Both termination circuits 46 and 57 also have access to their associated power supply slip rings for use as sinks in terminating their respective signal slip rings. Since the source impedance is nearly zero, both power source slip rings are at ac ground potential. Therefore, power slip rings are intermixed with signal slip rings to emphasize transmission line characteristics and prevent interference. Another advantage of this power distribution and isolation technique is that it eliminates common mode noise. Since the power conductor follows approximately the same path as the signal conductor, parallel to the signal conductor, external noise induces similar voltages in both conductors. As a result, as described below, even if inexpensive single-ended driving and receiving components are used, sufficient noise prevention and in-phase noise removal can be achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. Series input cable 47
has a pair of conductors 47a and 47b. Those conductors are connected to input drive circuit 45. The serial input signal on input cable 47 is a high data rate NRZI encoded signal. The actual encoding in stationary electronic equipment is
Micro Devices Advanced Micro
This is accomplished by an AM7968 integrated circuit encoder (not shown) manufactured by Microelectronic Devices, Inc. The decoding performed in the control circuit 27 upon reception is performed by an AM7969 type decoder (not shown) manufactured by Advanced Micro Devices. The same type of encoder and the same type of decoder can also be used for the outgoing communication described below.

The input signal on line 47 is connected to coupling capacitor 7
1 to the primary winding of the input transformer 70. This transformer provides DC isolation for the remainder of the input drive circuit 45 and inhibits the formation of an ac ground potential. Capacitor 71 is transformer 70
may become saturated. Functions to block DC current.

The primary winding of transformer 70 is also bypassed to shear sea earth 73 via capacitor 74 . It will be seen from the following description that the control of noise, particularly high frequency noise, is an important part of the invention. A shear-sea earth connection 73 is made to the metal parts that make up the structural frame of the CAT scanner 10.
Sea-earth connection 73 for all stages of the communication path
By adopting a configuration based on , the noise of the device can be significantly reduced. The capacitor 74 is
For high frequency AC signals, the primary winding of transformer 70 is placed at shear sea earth 73.

The secondary winding of the transformer 70 connects to the coupling capacitor 8
1 and a bias network comprised of resistors 82 and 83 to the input terminal of predriver stage 80. Predriver 80 preferably comprises standard CMOS integrated circuit inverters cascaded together. One input inverter provides signals to three parallel output inverters. A non-inverting predriver constructed thereby is used to maintain signal symmetry on positive and negative transitions, ie to provide equal delay for both polarities of transition. To configure the predriver 80
One CMOS octal inverter/driver integrated circuit type 74AC11240 is utilized.

The power supply voltage 80 for the predriver 80 is supplied via a voltage regulator 85 from the power supply voltage input cable 66 . The power supply voltage input cable 66 is +
It has one regulated dc input voltage of 12 volts labeled V and -V on lines 86 and 87, respectively. Line 87 with voltage -V is used as a common line for the amplifier stages in input drive circuit 45. The input to regulator 85 is + on line 86.
taken out from V. Regulator 85 is primarily used to allow operation of predriver 80 at standard logic voltages of 5 volts, with subsequent stages using the full supply voltage to achieve larger peak-to-peak output signal voltages. use In addition, since the power supply voltage is supplied in series to all of the communication drivers 45, 55 and receivers 48, 58, the power supply voltage is subject to some ohmic voltage drop, which is caused by transient phenomena caused by switching. May also include large spikes. Separated regulator 8
5 provides a noise-free stable voltage to the predriver 80 to prevent spurious state changes. Voltage regulator 8
It should be understood by those skilled in the art that 5 is understood to include an input bypass capacitor and an output bypass capacitor for wave purposes.

The output of predriver 80 is fed to the input terminal of driver stage 90. The driver 90 must have sufficient performance to drive a load equal to the net impedance of the slip ring 31b at the point of drive. From the transmission line analogy explained above, the net impedance at the driving point is
It can be viewed as half the impedance of either of the two parallel signal paths around the slip ring. Slip ring 3 in this example
1c to 31e, the net impedance is approximately 20 ohms (e.g., analogous to that shown in figure 1a, corresponding to a value of 40 ohms for the impedance of each branch, i.e. Z ₀ ). ) has been determined empirically. Therefore, driver 90 must drive an effective impedance of 20 ohms. Since the requirements for high speed operation and high drive performance are not currently available in integrated circuit implementation, driver 90 is preferably constructed from discrete components as shown in FIG.

Referring to FIG. 3, driver 90 is connected to lines 86 and 87.
It includes a totem-pole output stage formed by output transistors 100 and 101. Input transistor 102 receives the output of predriver 90 from input line 89 via a coupling capacitor 103 and a bias network comprised of resistors 104-106. To shorten the turn-off time of transistor 102, a resistor 10 is placed between the base and emitter of that transistor.
7 is connected. Transistor 107 operates to selectively turn one or the other of output transistors 100 and 101 into an "on" state. When input transistor 102 is turned off, for example by a low logic input, the base current of transistor 100 is supplied through the network formed by transistors 108 and 109, turning transistor 100 on. When transistor 102 is turned on, for example by a high logic input, transistor 100 is turned off and transistor 101 is provided with base current directly from transistor 102. The charge stored in the base of the transistor 101 is discharged through the resistor 110.

An important characteristic of driver 90, in addition to having sufficient drive performance, is that the output impedance of driver 90 matches the net impedance of the slip ring seen at the point of drive. The matched impedance at the driving point, in addition to the impedance-matched terminations described above, further reduces the possibility of energy reflections, e.g. due to varying impedances at the terminations or imperfect impedance matching, or from the load at the receiving connection. will decrease.

As mentioned earlier, the net impedance of the slip ring seen from the point of drive is approximately 20 ohms. Therefore, the impedance looking into driver 90 must also be approximately 20 ohms. Output resistance 1
12 is combined with the output transistor 100, and output resistors 113 and 114 are combined with the output transistor 101.
be combined with A desired output impedance can be achieved by appropriately selecting the resistance values of the output resistors 112-114. In particular, resistors 108 and 1
The resistance value of the parallel combination of 12 must be equal to 20 ohms (the output of the driver 90 is logically high) and consists of the series combination of resistors 113 and 114 and resistors 105, 106, 108-110. The combined resistance value of the parallel combination with the connected network should also be equal to 20 ohms (driver 9
An output of 0 is logically low).

Referring again to FIG. 2, the output terminal of the driver 90 on the line 120 is connected to the brush 125 in contact with the signal voltage transmission slip ring 31d at the driving point.
d via a capacitor 121. The ground reference slip ring 31c and the slip ring 31e are the same as the signal voltage transmission slip ring 31d.
on both sides and coaxially with it. The ground reference slip ring 31c is coupled to -V via a brush 125c, and the slip ring 31e is coupled to +V via a brush 125e. Since +V and -V are low impedance power supplies, the slip rings 31c and 31e are connected to the center slip ring 3.
Construct a ground plane for the signal on 1d, thereby providing the desired transmission line effects and some shielding from noise and crosstalk. Three slip rings 31c to 31e shown in FIG.
are shown with exaggerated axial separation for ease of illustration. In a preferred embodiment,
The thickness of each slip ring 31c-31e is approximately 4.8 mm (approximately 3/16 inch), and the thickness of the insulator between the slip rings 31c-31e is approximately 1.6 mm (1/16 inch).

Further referring to FIG. 2, input/termination circuit 46 is connected to slip rings 31c-31e via brushes 135c-135e, respectively. Each brush 1
35c to 135e are corresponding drive brushes 125
c~125e to slip rings 31c~31e
are located at diametrically opposed points across the In other words, the substantially colinear drive point brushes 125c-125e and the substantially colinear end point brushes 135c-135e are separated by 180 degrees about the slip rings 31c-31e, respectively. Brushes 135c and 135e are coupled to +V and -V power supply voltages at slip rings 31c and 31e, respectively. The incoming communication signal on the signal voltage transmission slip ring 31d is coupled to the incoming termination circuit 46 by the brush 135d at the termination point. In the input termination circuit, the + on line 136
The V supply voltage is bypassed by capacitor 138 to the -V supply voltage on line 137 and both lines 137
and 138 is the signal ground potential, i.e. line 137
-V, so that it exhibits a low ac impedance. A terminating resistor 140 serving as a resistive terminating portion is connected to the signal line 141 . The terminating resistor 1
The resistance value 40 is equal to the net impedance seen at the slip rings 31c-31e. As mentioned earlier, the net impedance of the slip ring, and therefore the preferred resistance value of the terminating resistor, is approximately
It is 20 ohms.

In practice, terminating resistor 14 and bypass capacitor 138 are preferably configured in multiple parallel devices to reduce net parasitic inductance and, in the case of terminating resistor 140, to increase power consumption.

-V in the input drive circuit 45 and input termination circuit 46
The power supply voltage constitutes the signal ground reference potential and the high voltage capacitors at brushes 125c and 135c/
Resistor network 145 is bypassed to shear sea earth 73. As mentioned above, Shear Sea Earth 7
Bypassing to 3 is important for equipment noise control. In particular, since drive circuit 45 and termination circuit 46 are DC isolated, biasing shear to sea earth 73 has been found to be important for satisfactory operation of the device. Also, since all brushes and all slip rings are "floating" with respect to DC,
It is necessary to provide a high resistance path between the slip ring system and the shear sea earth 73 as a DC reference to prevent static charge build-up. Network 145 therefore includes a resistive element in parallel with the capacitor.

Network 145 is also preferably configured to have a very high voltage breakdown rating. The reason for the high voltage rating is that in the preferred embodiment, the slip rings 31c-31d are connected to a plurality of other slip rings, including the three slip rings 31f-31h for the outgoing communication circuitry, as described below.
Other equipment installed in 1, especially the X-ray tube 15
is part of an assembly with a set of high voltage slip rings (not shown) for supplying power to the motor. Due to the close proximity of high voltage slip rings in the same assembly, short circuits can occur, for example, between the high voltage power supply and the slip rings 31c-31e or between the associated brushes 125c-125e and 135c-135e. . If a short circuit were to occur, a voltage on the order of 100 volts could be applied to any of the slip rings 31c-31e. Power supply voltage +V (line 86) and -V (line 87)
is not grounded and is, for example, "floating", so
Even if high voltage is accidentally applied, the bypass network 1
45, coupling transformer 70, 157, and power supply 65
As long as the "floating" range is properly rated, the part will not be damaged.

Referring now to FIG. 4, a preferred structure for high voltage bypass network 145 is comprised of two capacitors 146, 147 connected in series and resistors 148a-148h connected in parallel to the series capacitors. and a ladder-shaped resistor network. The capacitance of each capacitor 146 and 147 is 0.22〓F, and the rated voltage is 1000 volts. The capacitance of the series circuit of capacitors 146 and 147 is then 0.11 F and the rated voltage is 2000 volts (provided the voltage is equally distributed between capacitors 146 and 147). A resistor ladder network consisting of resistors 148a-148h has a tap between resistors 148d and 148e, which tap is connected to a series capacitor 1.
46 and 147 to facilitate equal voltage division between capacitors 146 and 147. Since the resistance value of each resistor 148a to 148h is 220K ohm, each capacitor 146
and 147 are shunted by 880K ohms, and the total resistance across the terminals of network 145 is 1.76M ohms.
To promote equal voltage division to capacitors 146 and 147, a resistive ladder network provides the high resistance path that provides the DC reference and provides a leader path for capacitors 146 and 147. A large number of individual resistors is preferred so that standard voltage rated resistors can be used.

Referring again to FIG. 2, an input/reception circuit 48 is provided in the gantry 11, and the slip rings 31c to 3
Rotates together with 1e. Therefore, the input/reception circuit is connected to the points 150c to 31c of the slip rings 31c to 31e.
It is physically connected to slip rings 31c-31e at 150e. Points 150c to 150e are on a straight line. Signal line 151 is slip ring 3
1d and is coupled to the input terminal of buffer 152 via series resistor 153 to capacitor 154 and bias resistors 155a and 155.
Combine b. Connection point 1 of slip ring 31d
It is important to make the impedance of signal line 51 as high as possible so as to minimize reflections at 50d. The bridging impedance, i.e.
The impedance of the signal line 151 seen at the connection point 150d is at least 10 of the characteristic impedance Z ₀ .
Preferably, it is doubled. In this example, the characteristic impedance Z ₀ is approximately equal to 40 ohms, so the bridging impedance seen at connection point 150d must be higher than 400 ohms.
Even though the DC input impedance of buffer 152 is very high, the buffer has some input capacitance that causes it to exhibit a lower AC impedance. Therefore, signal line 1 seen at connection point 150d
A series resistor 153 is used to increase the impedance of 51. It has been found that a resistance value of 200 ohms is satisfactory for the series resistor 153.

The output terminal of buffer 152 is capacitor 156
is coupled to the primary winding of isolation transformer 157 via. The secondary winding of transformer 157 is capacitor 1
58 to serial output cable 49. This output cable transfers input serial data to the control unit 2.
Combine to 7. One leg of transformer 157 is bypassed to shear sea earth 73 via capacitor 159. The output coupling of this transformer is as described above for the input drive circuit 45.
Perform DC isolation of slip-ring systems and prohibit the formation of AC ground loops.

In addition to the above data transmission function, the input/reception circuit 48
supplies the DC operating voltage to the outgoing communication path. Supply voltages -V and +V are picked up by leads 160 and 161 at connections 150c and 150e, respectively, of slip rings 31c and 31e, respectively.

A voltage regulator 85 connects the power supply voltages +V and -V present on lines 161 and 160, respectively. The voltage regulator 85 transfers the regulated power supply voltage to the buffer 15.
2 and the associated bias resistor 15
5a and 155b. Power supply voltage +V and -V
are also supplied to inductors 163 and 164 and become +V' and -V', respectively. The symbols +V' and -V' have been used to indicate the AC decoupling effect provided by inductors 163 and 164. The power supply voltages +V' and -V' are supplied to the incoming signal via cable 67, as described below.

Refer now to FIG. The outgoing channel represents a second embodiment of the invention. In this embodiment, the output drive circuit 55 and the output termination circuit 57 are connected to the rotating gantry 1.
1 and is physically connected to the second coaxial slip ring set 31f to 31h. The output/reception circuit 58 is stationary, and the brushes 165f to 165
It is coupled to slip rings 31f to 31h via h. This embodiment shows the principle of terminating the applied signal to a point 180 degrees different from the drive point, and unlike the brush in the first embodiment, the slip ring 31 is physically terminated. The connection provides a drive point and a termination point.

Each configuration of the output drive circuit 55, output termination circuit 57, and output/reception circuit 58 is the same as the corresponding input drive circuit 45.
, the input/termination circuit 46 , and the input/receive signal circuit 48 have almost the same configuration, and the same parts are designated by the same reference numerals. Since the configurations and functions of the input and output circuits are similar, only the differences will be explained below.

Output drive circuit 55 receives operating voltages +V' and -V' from input/reception circuit 48 via cable 67.

Lines 170, 17 for operating voltages +V' and -V'
1 is connected to slip rings 31f, 31h at points 172f and 172h. Outgoing communication signals are received from the control section 27 via the input cable 56. The serial output signal from the output drive circuit 55 is on line 1.
Slip ring 31 for signal voltage transmission via 73
g is applied by electrical connection 172g at the driving point. All connection points 172f to 172h are substantially on the same straight line.

The line 176 connected to the outgoing termination circuit 57 is connected to the signal voltage transmission slip ring 31g by an electrical connection 180g at its termination point. similar line 1
75, 177 is the normal physical electrical connection 180f, 1 at the termination point to the slip ring 31f, 31h.
Connected by 80h. Electrical connection 180f~
Point 180h connects connections 172f to 172h for output drive circuit 55 according to the above principle of the invention.
The positions are 180 degrees different.

The stationary output/reception circuit 58 includes brushes 165f~
165h through each slip ring 31f.
~31h, the communication signal on the signal voltage transmission slip ring 31g and the power supply voltage -V' of the ground reference slip ring 31f,
It receives the power supply voltage +V' on the slip ring 31h. Communication signals are detected as described above and coupled to stationary electronics 30 via cable 59. The power supply path does not extend beyond the output/reception circuit 58, thereby avoiding the formation of ground loops that could cause oscillations or couple noise.

A final note on circuit arrangement: Due to the high frequencies involved, it is preferred to have all active circuitry as close as possible to the point of contact to the slip ring. In particular, in a preferred embodiment, the input slip rings 31c to 31e and the output slip rings 31f to 31h are provided close to each other. Input drive circuit 45 and output/reception circuit 58 are correctly physically positioned relative to the brush assembly including brushes 125c-125e and 165f-165h. Similarly, the input/reception circuit 48 and the output drive circuit 55
and out-termination circuits 57 are located in close proximity to the connection points to the respective slip rings.

It will be obvious to those skilled in the art that the embodiments of the present invention described above can be modified in various ways without departing from the gist of the present invention. For example, although the slip ring has been described as rotating with the gantry 11, it is equally possible for the slip ring to be stationary and the brush to be mounted on the gantry. In the latter case, the brush can contact the inner circumferential surface of the slip ring. In other words, the stationary mechanism and the rotating mechanism can be thought of interchangeably as mere platforms that are arranged to move in rotation relative to each other.

It is also contemplated by the present invention that the physical connection to the slip ring in the above embodiments may be replaced by a brush, eg, all contact to the slip ring may be made with a brush. In that way, the slip ring does not have to be fixed to any platform, but can instead be "freely rotated."

Finally, the actual diameter of the slip ring can vary significantly from the approximately 4 feet shown in the above embodiment. CAT scanners are also known in industrial applications, for example for flaw detection in components. Such industrial CAT scanners do not require the patient to be physically exposed, so they can be much smaller than medical CAT scanners. Therefore, much smaller slip rings can be used. In that case, it should be recognized that the principles of the invention are still required at high data rates.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a computerized axial tomography (CAT) scanner using the high-speed communication device of the present invention, and FIG. 1a is a schematic diagram showing an equivalent transmission line of a slip ring used in the communication device of FIG. , FIG. 2 is a schematic diagram of an input communication circuit forming part of the high-speed communication device shown in FIG. 1, and FIG. 4 is a detailed diagram of the high-voltage bypass circuit network that forms part of the input communication circuit in Figure 2 and the output communication circuit in Figure 5. Figure 5 is a detailed diagram of the high-speed communication circuit in Figure 1. 1 is a schematic diagram of an outgoing communication circuit forming a part; 14...unit, 25...rotating electronic device, 30...stationary electronic device, 31...slip ring, 46...input termination circuit, 45...input drive circuit, 48...input/reception circuit, 55...output drive circuit , 57... output termination circuit, 58... output/reception circuit, 70... transformer.

Claims (1)

[Scope of Claims] 1. A stationary electronic device 30 provided on a stationary table, and a rotating table 11 provided on a rotary table 11 capable of performing rotational movement about a rotation axis with respect to the stationary table. A communication device that performs high-speed communication with the movable electronic device 25, which includes: a communication device provided on the rotating table 11 coaxially with the rotating shaft;
A slip ring 31d for transmitting a signal voltage is provided; a drive circuit 45 connected to the stationary electronic device 30 and provided on a stationary stand is connected to the stationary electronic device 30;
A drive circuit 45 that sends an electric signal voltage encoded with the data to be communicated from and based on the signal ground reference potential to the signal voltage transmission slip ring 31d.
The drive circuit 45 is configured to drive the signal voltage transmission slip ring 31 within the reference frame of a stationary stand.
It is slidably connected to the signal voltage transmission slip ring 31d by a brush 125d which makes sliding electrical contact at its drive point 40 with respect to the signal voltage transmission; A termination circuit 46 for terminating the electrical signal voltage on the slip ring 31d for signal voltage transmission is provided, and the termination circuit 46 is slidable at its termination point 44 with respect to the slip ring 31d for signal voltage transmission within the reference frame of a stationary stand. The signal voltage transmission slip ring 31d is slidably connected to the signal voltage transmission slip ring 31d by a brush 135d that makes electrical contact with the signal voltage transmission slip ring 31.
d, the termination circuit 46 including a resistive termination 140 connected between the brush 135d located at the termination point and a signal ground reference potential; 11, which receives the electrical signal voltage on the signal voltage transmission slip ring 31d and sends it to the mobile electronic device 25, and an electrical connection 150 to the signal voltage transmission slip ring 31d.
A communication device characterized in that it is equipped with a receiving circuit 48 having the structure shown in FIG. 2. In the communication device according to claim 1; The rotary table 11 is provided with a ground reference slip ring 31c coaxially with and close to the signal voltage transmission slip ring 31d; Earth reference slip ring 31c. In order to apply the signal ground reference potential to 31c, the drive circuit 45:
The ground reference slip ring 31c is connected to the ground reference slip ring 31c within the reference frame of the stationary table by a brush 125c that is slidably in electrical contact with the ground reference slip ring 31c at a point substantially on the same straight line as the driving point. The terminal circuit 46 is slidably connected to the earth reference slip ring 31c within a reference frame of a stationary table at a point substantially colinear with the terminal point.
It is slidably connected to the earth reference slip ring 31c by a brush 135c that makes electrical contact in a slidable manner, and the point is substantially colinear with the driving point and the terminal point is substantially colinear with the terminal point. The points are located substantially diametrically opposite each other with respect to the ground reference slip ring 31c, and the signal ground reference potential used for the resistive termination is from the brush 135c located at the point substantially colinear with the termination point. A communication device characterized by the following: 3. A stationary electronic device 30 provided on a stationary table and a movable electronic device 25 provided on a rotary table 11 that can perform rotational movement about a rotation axis with respect to the stationary table. A communication device that performs high-speed communication between: a communication device provided on the rotating table 11 coaxially with the rotating shaft;
A slip ring 31g for signal voltage transmission; connected to the movable electronic device 25 and connected to the drive circuit 55 provided on the rotary table 11;
A drive circuit 55 that sends an electric signal voltage that is encoded with data to be communicated from and that is based on the signal ground reference potential to the signal voltage transmission slip ring 31g.
This drive circuit 55 is equipped with a signal voltage transmission slip ring 31 within the reference frame of the rotary table 11.
electrical connection 172 at its driving point to g
g; equipped with a termination circuit 57 provided on the rotary table 11 and terminating the electric signal voltage on the signal voltage transmission slip ring 31g; Electrical connection 180g is made to the voltage transmission slip ring 31g at its terminal point, and the driving point and the termination point are connected to the signal voltage transmission slip ring 31g.
are located almost diametrically opposite each other,
The termination circuit 57 includes a resistive termination 140 connected between the electrical connection 180g at the termination point and a signal ground reference potential; a slip ring mounted on a stationary platform for transmitting the signal voltage. The receiving circuit 58 receives the electrical signal voltage above 31g and sends it to the stationary electronic device 30, and the brush 165g slidably makes electrical contact with the signal voltage transmission slip ring 31g. A communication device comprising a receiving circuit 58 that is slidably connected. 4. In the communication device according to claim 3; The rotary table 11 is provided with a ground reference slip ring 31f coaxially with and close to the signal voltage transmission slip ring 31g; In order to apply the signal ground reference potential to 31f, the drive circuit 55
An electrical connection 172f is made to the ground reference slip ring 31f within the reference frame of the rotary table 11 at the point on the same line as the driving point; An electrical connection 180f is made to the reference slip ring 31f at the point on the same straight line as the terminal point, and the point on the same straight line as the driving point and the point on the same straight line as the terminal point. are substantially diametrically opposed to each other in the ground reference slip ring 31f, and the signal ground reference potential used for the resistive termination is obtained from the electrical connection 180f at a point substantially collinear with the termination point. A communication device characterized by: